Main diagonal of square array A137570.

Terms

a(0) =1a(1) =2a(2) =10a(3) =60a(4) =397a(5) =2802a(6) =20710a(7) =158428a(8) =1244413a(9) =9980220a(10) =81394123a(11) =672998498a(12) =5628741195a(13) =47535483498a(14) =404790717079